A distribution power combiner of such a type as explained in the Microwaves & RF vol. 8, pp 107-112 1998 has been known as a power combiner applied to a power amplifier of a cellular base station. FIG. 18 shows a circuit configuration of the conventional distribution power combiner. A combining number will be defined as n. A RF signal applied from an input terminal 7 is distributed to respective amplifiers 101-1 through 101-n by branch circuits 103-1 through 103-(n-1) in sequence. The RF signals amplified by the respective amplifiers 101 are sequentially combined into one by combiners 102-1 through 102-(n-1), after which the combined one is outputted to an output terminal 8.
In order to bring out the full linearity of a semiconductor device used in each amplifier 101, it is desirable to reduce the maximum power inputted to each amplifier 101, i.e., equalize respective power inputted to the respective amplifiers 101. At this time, the power to be amplified by the respective amplifiers 101 become equal to each other.
Power distribution ratios for equalizing the power inputted to the respective amplifiers 101 are represented every branch circuits. If power inputted to an input transmission line 106 from the input terminal 7 is defined as n, it is then necessary to distribute power to be inputted to the first amplifier 101-1 and power to be inputted to the second branch circuit 103-2 in a ratio of 1:(n-1). Distribution ratios to other branch circuits are determined in a similar relationship.
On the other hand, if power outputted from the output terminal 8 through an output transmission line 107 is defined as n, it is then necessary to combine first power outputted from the nth amplifier 101-n and (n-1)th power outputted from the n-1th combiner 102-(n-1) into one. Distribution ratios to other combiners are determined in a similar relationship.